1. Field of the Invention
The present invention relates to nanoparticles provided with a lamellar coating consisting of a silicone surfactant, and to their use in a composition, in particular in a topical composition for treatment of the skin, mucosae, nails, scalp and/or hair.
2. Description of the Background
It is known in the cosmetic and dermatological fields, for example from EP-A-557489, EP-A-447318 and WO-A-93/25195, to apply to the skin active agents trapped in spherules in order to improve the efficacy of these active agents. These spherules are, in particular, nanoparticles of polymer, the small size of which, of the order of 10 to 1000 nm, permits better penetration into the upper layers of the epidermis. The term nanoparticles encompasses on the one hand nanospheres and on the other hand nanocapsules. "Nanospheres" denotes nanoparticles consisting of a porous polymer matrix on which the active agent is absorbed and/or adsorbed, and "nanocapsules" denotes nanoparticles consisting of a polymer membrane which encapsulates an oily core.
When nanoparticles are incorporated in compositions, a release of the active agents into the composition frequently takes place. In the particular case of nanocapsules, when they are incorporated in a composition containing an oily phase, such as for example emulsions, the active agents encapsulated in the oily core migrate to the oily phase of the composition. This premature release of the active agents into the composition makes their encapsulation in nanoparticles ineffective.
To remedy this drawback, it is known to coat the nanoparticles with a lamellar phase. Hitherto, in order to obtain a coating having sufficient freedom from leakage, a lecithin-based lamellar coating was used, as described in EP-A-447318. In point of fact, lecithin possesses the drawback of being sensitive to oxidation, which results in a yellowing of the nanoparticles, imparting to the composition containing them an appearance which is rather distasteful to the user.
The need hence remains for nanoparticles provided with a lamellar coating having good freedom from leakage and not possessing the drawbacks mentioned above.
Applicants have found, unexpectedly, a lamellar coating enabling this objective to be achieved.